U.S. health officials say swine flu could strike up to 40% of Americans over the next two years and as many as several hundred thousand could die if a vaccine campaign and other measures aren't successful. Those estimates from the Centers for Disease Control and Prevention mean about twice the number of people who usually get sick in a normal flu season would be struck by swine flu. Officials said those projections would drop if a new vaccine is ready and widely available, as U.S. officials expect.